Spin-Orbital Entangled Excitonic Insulators in $(t_{2g})^4$ Correlated Electron Systems

TL;DR

This study uses multi-orbital dynamical mean-field theory to explore how strong correlations and spin-orbit coupling create novel nonmagnetic and magnetic excitonic insulators in a three-orbital electron system, with observable spectral features.

Contribution

It reveals the emergence of multiple excitonic insulator phases driven by electron correlations and spin-orbit coupling in a $(t_{2g})^4$ system, expanding understanding of correlated spin-orbital physics.

Findings

Identification of a Van Vleck-type nonmagnetic insulator with magnetic exciton condensation.

Discovery of a new nonmagnetic excitonic insulator induced by spin-orbit coupling.

Spectral features indicative of these insulators are accessible via ARPES experiments.

Abstract

We employ the multi-orbital dynamical mean-field theory to examine the ground state of a three-orbital Hubbard model with a relativistic spin-orbit coupling (SOC) at four electrons per site. We demonstrate that the interplay between the strong electron correlations and the SOC induces a Van Vleck-type nonmagnetic insulator and its magnetic exciton condensation. We also find in the moderate electron correlation regime that the SOC induces another type of a nonmagnetic excitonic insulator, in addition to a relativistic band insulator. The characteristic features among these insulators are manifested in the momentum resolved single-particle excitations, thus accessible by angle-resolved photoemission spectroscopy experiments.